Sexual reproduction Two parents- each parent contributes half of its genetic information to the offspring Maintains variety within a species

Review- chromosomes are found in pairs called homologous chromosomes Diploid chromosomes number – both chromosomes from each pair are present in the cell

Monoploid chromosome number- only one chromosome from each pair is present in the cell. (also called haploid chromosome number)

Meiosis Occurs only in the gonads Produces gametes with a monoploid (n) chromosome number

Gonads- specialized structures where meiosis occurs Testes ovaries

Gametes- specialized cells with a monoploid chromosome number Sperm Ova (eggs)

Spermatogenesis Is Meiosis in the male Produces sperm Occurs in the testes All sperm have an adaptation that allows them to travel to the egg

Oogenesis Is meiosis in the female Produces eggs (ova) Occurs in the ovaries

Sperm + Egg= Zygote n+n=2n Fertilization Sperm + Egg= Zygote n+n=2n

External fertilization Occurs outside the female body Fish and amphibians Many ova are released at one time. Sperm are deposited over the eggs

Internal fertilization Occurs inside the female body Sperm is introduced into the moist environment of the female reproductive tract where they unite with the ovum (egg)

External development Occurs outside the female body Amphibians, fish: develop in water Yolk provides food Little or no parental care Birds, reptiles: fertilization occurs before shell forms yolk, nest

Internal development Occurs inside female body

Non-placental mammals platypus

Marsupials Have an underdeveloped placenta

Give birth to premature offspring that climb in a pouch (marsupium) to finish their development

External development vs. Internal development worksheet

Human Reproduction Males-

Testes- male gonads; lie outside the body in the scrotum where the temp. is 2-4o lower than body temp. Sperm produced continuously from puberty to old age. Epididymis- coiled tube that stores and nourishes sperm; flagellum (tail) grows

Vas deferens- sperm duct that leads from the epididymis to the urethra Seminal vesicles, Cowper’s gland & prostate- all produce fluid which becomes semen

Females

Ovaries – female gonads; where ova are produced; 1 ½ inches long; in lower abdominal cavity Fallopian tubes (oviduct)- lead from ovary to uterus * Fertilization occurs here!!!! Uterus- pear-shaped organ, thick walled, muscular. Development of fetus occurs here

Cervix- muscular ring between uterus and vagina Vagina- muscular tube leading from uterus to outside the body. (birth canal)

Menstrual cycle Female releases one gamete (ovum) once a month from puberty to menopause Controlled by hormones 4 stages

Follicle stage Follicle – structure in the ovary where the ovum is prepared to be released Last 10- 14 days FSH (follicle stimulating hormone) from the pituitary causes the formation of the follicle Follicle begins to release the hormone estrogen which shuts off the production of FSH Estrogen triggers the thickening of the uterine lining

Ovulation Ovum is released from the ovary Luteinizing hormone (LH)- triggers ovulation

Corpus luteum Follicle fills with yellow cells that produce a hormone called progesterone Progesterone maintains the thickening of the uterine lining in case fertilization occurs

Menstruation Uterine lining is shed if fertilization does not occur

Fertilization Occurs in the upper part of the Fallopian tube Sperm and egg unite; diploid chromosome number is restored

Embryonic Development Embryology- study of embryo development

Terms in embryology Zygote – fertilized egg Cleavage- rapid cell division in zygote; division of zygote into a solid ball of cells Morula- solid ball of cells

morula

Blastula- hollow ball of cells- differentiation begins in this stage of development Differentiation – cells become specialized in structure and function

blastula

Gastrula- formation of 3 primary germ layers

gastrulation

3 primary germ layers These 3 layers of cells develop into the structures of the new organism

endoderm Inner most layer of cells Produces digestive tract Respiratory system Liver Pancreas thyroid

mesoderm Middle layer of cells Produces Skeleton Muscles Circulatory system Excretory system gonads

ectoderm Outer layer of cells Produces Nervous system Skin Hair

Life in the uterus Placenta forms from embryonic cells Exchange of materials between mother and fetus Mother sends oxygen, food, antibodies to fetus Fetus sends waste to mother (Carbon dioxide, urea) No exchange of blood

Umbilical cord forms between the 4th and 8th week

Amnion- membrane that holds amniotic fluid (protection) Umbilical cord- connects placenta to fetus

4 weeks

8 weeks

3 months

6 months

6 months

Multiple births More than one child born at a time

Identical Twins One egg is fertilized by one sperm and in early embryonic development the morula splits into two individual group of cells. Can identical twins be two different genders?

Fraternal twins Two eggs are fertilized by two different sperm

Caesearn section Surgery is performed to remove the fetus from the uterus.